In the Parisian location shots, Simon is driving an orange Citroen. In the studio and outside shots in England, his Citroen is cream.
A joke rather than a mistake: the temperature gauge in the steam room goes from 'Froid' to 'Ouarm' to 'Chaud'. While 'Froid' and 'Chaud' are the French words for cold and hot, 'Ouarm' is not a French word at all - but would be pronounced 'warm' if it were.
In the underground garage scene, as Simon drives away, the 'floor' is revealed to be obviously a sheet of carpet or tarpaulin.